Electron discharge device having an exchangeable electrode



April 4, 1967 R. J. MELLING ELECTRON DISCHARGE DEVICE HAVING AN EXCHANGEABLE ELECTRODE Filed Jan. 4, 1965 nza-44 42 3a Fig. 2.

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GQQHL 3- INVENTOR Richard J. Melling ATTORNEY United States Patent Otiiice n 3,312,855 Patented Apr. 4, 1 967 3,312,855 ELECTRON DISCHARGE DEVICE HAVING AN EXCHANGEABLE ELECTROBE Richard J. Melting, Veteran, N.Y., assigner to Westinghouse Electric Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Filed Jan. 4, 1963, Ser. No. 249,497 4 Claims. (Cl. 313-237) This invention relates generally to electron discharge devices and, more particularly, to a replaceable filamentary cathode assembly for use in electron discharge devices.

While the present invention has particular application in the iield of ionization vacuum gauges of the Bayard- Alpert type and will be described with respect to such devices, it is not so limited and does, in fact, enjoy application in any type of electron discharge device ernbodying a ilamentary type cathode in which it may be desirable, from time to time, to replace this filament. In 4United States Letters Patent No. 2,605,431, issued July 29, 1952, assigned to the assignee of the present invention, there is described an ionization vacuumgauge of the general type to which the present invention has particular application. The device therein shown, which is known in the industry as the Bayard-Alpert gaugeincludes Within an envelope a centrally disposed thin Wire electrode which acts as the ion collector. An accelerating electrode, inthe form of a grid, is disposed about the ion collector. Positioned exteriorly to the accelerating electrode is a lamentary type of cathode. Means` are provided whereby the envelope is connected to the vacuum system. In operation, the cathode is heated and caused to emit electrons which, when they strike gas molecules, produce ions. These ions are collected on the ion collector and a measure of the current owing Within the collector circuit is an indicium of the amount or pressure of the gas within the vacuum system.

Since the advent of gauges of this nature, it has become the practice in certain instances to omit the envelope and to build the electr-ode assembly onto a base structure which is tted directly onto the vacuum system itself. Thisy is the so-called nude ionization vacuum gauge.

In devices of this nature, including both those with and Without envelopes, the life of the tube has normally been limited by the life of the lilamentary cathode. In the case of devices including an envelope, it has Ibeen common practice to place multiple cathodes within the device and to sequentially utilize these cathodes to prolong the total life of the ionization vacuum gauge However, with the introduction of the nude type gauge, the accessibility of the electrodes has made filament replacement a possibility without the extensive rebuilding of the tube. While filament replacement is, per se, old in the art, the general practice with these gauges has been that the user must have recourse to the vendor or to other skilled personnel for replacement. This procedure is, obviously, cumbersome and expensive. It is desirable therefore, that the filament replacement be capable of being performed by the user and that such replacement not require special skills or equipment at the users location. It is, therefore, an object of this invention to provide an improved electron discharge device.

A further object is to provide an improved electron discharge device employing a replaceable iilament. l Still another object is to provide an improved replacement ilament for use in an electron discharge device.

Another object is to provide an improved ionization vacuum gauge. l

A still further object is to provide an ionization vacuum gauge in which the filamentary cathode may be replaced by the user with a minimum of skill and equipment.

Stated brielly, the present invention provides an electron discharge device having an electrode assembly supported from a base. Included within this electrode assembly is a replaceable electron emissive filament which is preformed at the place of manufacture and forms a part of a sub-assembly which is removably secured to support leads extending from the base. `The sub-assembly allows the preforming of the iilament and shipment to the place of use.

Further objects and advantages of the invention will become apparent as the following description proceeds and features of novelty which characterize the invention will be pointed out in particularity in the claims annexed to and forming a part of this specification.

For a better understanding of the invention, reference may be had to the accompanying drawings, in which:

FIGURE 1 is a perspective view, partially broken away, of an ionization vacuum gauge embodying the present invention;

FIG. 2 is a side elevational view, partially exploded, of a filament sub-assembly in accordance with the present invention;

FIG. 3 is a top plan View of one of the elements of the sub-assembly of FIG. 2;

FIG. 4 is a side elevational view illustrating the lilament sub-assembly of FIG. 2 as it is to be utilized in the device of FIG. l; and

FIG. 5 is a top plan view of a portion of an electrode assembly illustrating one of the features of the present invention. t

With reference now to FIG. 1, there is shown an ionization vacuum gauge embodying the present invention. As illustrated, the guage is of the nude type, that is, it does not have its own envelope but is instead designed to be inserted into the Vacuum system in which it is to operate. The device includes a base 10 having a plu'- rality of holes 16 provided therein. Suitable fastening means such as bolts (not shown) extend through the holes 16 and serve to affix the base, and hence the ionization vacuum gauge, to the vacuum system in which the gauge is to be utilized. Suitable gasket means (not shown) may be used between the top surface of the base 10 and the exterior wall of the vacuum system in order to provide a vacuum tight seal between these two elements.

An electrode assembly, indicated generally at 20, is positioned atop the Ibase 10. Centrally disposed within this electrode assembly 20 is an ion collector electrode 22 which may be a thin wire of electrically conductive material. Substantially surrounding the ion collector electrode 22 is a grid or accelerator electrode 24. The accelerator electrode 24 may consist of a thin wire mesh curved about the collector electrode and separated substantially therefrom, or as is shown in the d-rawing, it may consist merely lof a plurality of turns of line wire surrounding the collector electrode 22. The accelerator electrode 24 is supported by one or more supporting Wires 26 which extend into the base 10. The supporting Wires 26 may also `be employed to supply a potential to the accelerator electrode 24. External to the acceleration electrode 24 but also supported from the base 10 is a cathode assembly 30 which is inclusive of a ilamentary cathode sub-assembly 32, the sub-assembly 32 including a filament 34. As is standard in the art, means are included which extend through the base 10 whereby the electrodes may be provided with suitable electrical potentials.

In the operation of the above-described apparatus, electrons emitted from the filament 34 are accelerated by the acceleration electrode 24 toward that electrode.

`Since the acceleration electrode 24 consists of a num-ber of turns of fine wire separated from each other by a substantial space, most of the electrons will pass through the acceleration electrode 24 into the region inside that electrode. Due to the potential applied to the several electrodes of the electrode assembly 2f), these electrons are caused to oscillate and in so doing collide with gas molecules which are present within the vacuum system. Upon collision, the gas molecules are ionized and these gas ions are collected by the ion collector electrode 22. A measure of the current at electrode 22 is indicative of the amount of gas within the vacuum system. A more complete description of the general nature and operation of these devices may be found in the aforementioned Bayard Patent No. 2,605,431.

The filamentary cathode sub-assembly 32 of the present invention, as it appears prior to insertion into the device of FIG. l, may best be seen with respect to FIGS. 2 and 3. The sub-assembly 32 comprises a mounting rod 36 the ends of which may be provided with screw threads 42. Near each end of the mounting rod 36 there is provided a transverse support member 38 which is secured to the mounting rod 36 yby a suitable means such as brazes 40. In the illustrated embodiment, the transverse support members 38 are in the form of plates each having an aperture 41 near one end thereof. This aperture 41 is dimensioned such that the mounting rod 36 may be inserted within the aperture prior to the brazing. The support members 38 are securely fastened to the mounting rod 36 and in the specific embodiment shown extend substantially perpendicular to the longitudinal axis of the mounting rod 36. Positioned at the other ends of the transverse supporting members 38 and extending therebetween is a filament 34 of a suitable material, for example tungsten, which is capable of electron emission upon being heated. The ends of the filament 34 are affixedto the two transverse support members 38 by any suitable means, for example, welding or brazing.

The sub-assembly 32, as it is shown in FIG. 2, is one which may 'be assembled at the point of manufacture and, because of its particular configuration, shipped as a unit with the filament 34 properly formed for subsequent insertion into a device such as is shown in FIG. l.

With reference once again to FIG. 1 and also referring now to FIG. 4, there is shown the sub-assembly 32 after it has been inserted into the device and then made ready for operation within the device. There is provided extending substantially vertically from base 10, two support leads 46 and 47 of electrically conductive material. The support leads 46 and 47 are spaced from one another and preferentially have a height differential slightly greater than the length of the filament 34. Near the upper end of each of the support leads 46 and 47 and extending transversely to the longitudinal axes thereof, there are provided two connecting members 48 and 49. These connecting members extend respectively from the support leads 46 and 47 and are rigidly secured thereto by suit- :able means such as welding. The outer ends of each of the connecting members 48 and 49, in the illustrated embodiment, are provided with an aperture of sufficient dimension to accommodate the insertion of the mounting rod 36. The subassem'bly 32 is positioned within the ydevice by inserting the threaded end portions 42 of the mounting rod 36 into the apertures provided in each of the connecting members 48 and 49. Suitable nuts 44 are then threaded onto the screw threads 42 and after the filament 34 has been properly positioned with respect to the accelerator electrode 24, the nuts 44 are tightened to provide a good mechanical connection as well as electrical connection between the connecting mem-bers 48 and 49 and the transverse support members 38. (It is, of course, obvious that this method of retention is only illustrative and that any suitable method and means may be utilized.)

The feature of positioning the filament 34 with respect to the accelerator electrode 24 is best shown in FIG. 5.

As is known to those skilled in the art, the proper operation of a device such as has been described is dependent upon many conditions or factors including the electrode voltages. For any given set of conditions there is an optimum spacing between the filament 34 and the accelerator electrode 24. This distance is represented by X in FIG. 5. That this distance X is easily adjustable through the use of the present invention is obvious. Prior to the tightening of the nuts 44 the entire sub-assembly 32 is easily pivoted about the longitudinal axis of the mounting rod 36 and, through the utilization of any suitable measuring device, the filament 34 may be properly positioned with respect to the accelerator electrode 24.

After the nuts 44 have been tightened to hold the filament 34 securely in place, the mounting rod 36 is severed and a portion of that rod which is positioned between the two transverse support members 38 removed. Preferably, the rod 36 is severed near each of the two brazes 48 and the whole central portion removed. This removal of the center portion of the rod 36 provides that theA only electrical path now existing between the two vertical support leads 46 and 47 is through the filament 34.

Thus it is seen that, by the present invention, there has been provided a replaceable filamentary cathode structure which may be formed and assembled at the manufacturers location and shipped to points of use; at which points the new filament may be inserted and positioned within the device by personnel having a minimum amount of skill and tools. Thus, as it is the filament in devices such as this which is often the limiting factor in the life of the device, by this simple expediency the life has been greatly increased.

While there have been shown and described what are at present considered to be the preferred embodiments of the invention, modifications thereto will `readily occur to those skilled in the art. For example, while the device has been described with `respect to a mounting rod made presumptively of metal and while the use of metal as this rod would appear to be the most practical solution, it is readily conceivable that this rod could be made out of a non-electrically conductive material and thus the removal of the central portion of this rod would not be necessary. It is not desired, therefore, that the invention be limited to the specific arrangements shown and described and it is intended to cover in the appended claims all such modifications as fall within the true spirit and scope of the invention.

I claim as my invention:

1. An electron discharge device comprising first and second support members for receiving an electrode subassembly, said electrode sub-assembly including third and fourth support members adapted to be engaged respectively to said first and second support members, a replaceable filament disposed between and connected to said third and fourth support members, an intermediate member disposed between said third and fourth support members for tensioning said filament prior to insertion Within said electron discharge device, said intermediate member havng a frangible portion which may be removed so that said filament is placed under tension by said first and second support members.

2. An ionization gauge comprising a base and an electrode assembly supported from said base, said electrode assembly including an ion collector, an accelerator electrode and a cathode assembly, said cathode assembly comprising first and second support members extending from said base and a filament sub-assembly disposed between said first and second support members, said filament subassembly including a mounting rod, third and fourth support members affixed to said mounting rod and a filament extending between sai-d third and fourth support members, said mounting rod having a frangible portion which may be removed so that said filament is placed under tension by said first and second support members, and means for removably connecting said third and fourth support members to said rst and second support members thereby permitting the removal of said frangible portion of said mounting rod.

3. A replacement electrode assembly comprising rst and second support members, a filament disposed between and connected to said first and second support members, an intermediate member disposed between said lirst and second support members for tensioning said filament prior to insertion within an electron discharge device, said first and second support members adapted to be engaged to a support structure of the electron discharge device, said intermediate member having a frangible portion thereof to be removed so that said lament is only supported under tension by the support structure of the electron discharge device.

4. A replacement electrode assembly comprising first and second support members, a lament disposed between and connected to said first and second support members, an intermediate member disposed between said rst and second support members for tensioning said lament prior to insertion within an electron discharge device, and means for removably connecting said rst and second support members to a support structure of the electron discharge device, said intermediate member having a frangible portion to be removed so that said lament is only tensioned by the support structure of the electron discharge device.

References Cited by the Examiner UNITED STATES PATENTS 973,157 10/1910 Bering 313--237 1,031,114 7/1912 Gilmore 313-227 X 1,082,587 12/ 1913 Greengard 313277 1,666,450 4/1928 Holweck 313-237 X 2,176,087 10/1939 Machler.

2,352,635 7/1944 Irwin 313--278 X 2,475,988 7/1949 Rodd 313--279 X 2,829,337 4/ 1958 Groendijk 313-7 3,183,395 5/1965 Rively et al. 313-333 X FOREIGN PATENTS 697,823 9/ 1953 Great Britain.

JOHN W. HUCKERT, Primary Examiner. A. J. JAMES, Assistant Examiner. 

1. AN ELECTRON DISCHARGE DEVICE COMPRISING FIRST AND SECOND SUPPORT MEMBERS FOR RECEIVING AN ELECTRODE SUBASSEMBLY, SAID ELECTRODE SUB-ASSEMBLY INCLUDING THIRD AND FOURTH SUPPORT MEMBERS ADAPTED TO BE ENGAGED RESPECTIVELY TO SAID FIRST AND SECOND SUPPORT MEMBERS, A REPLACEABLE FILAMENT DISPOSED BETWEEN AND CONNECTED TO SAID THIRD AND FOURTH SUPPORT MEMBERS, AN INTERMEDIATE MEMBER DISPOSED BETWEEN SAID THIRD AND FOURTH SUPPORT MEMBERS FOR TENSIONING SAID FILAMENT PRIOR TO INSERTION WITHIN SAID ELECTRON DISCHARGE DEVICE, SAID INTERMEDIATE MEMBER HAVING A FRANGIBLE PORTION WHICH MAY BE REMOVED SO THAT SAID FILAMENT IS PLACED UNDER TENSION BY SAID FIRST AND SECOND SUPPORT MEMBERS. 